In a string of breakthrough roles, Jessica Chastain has already wowed critics and audiences alike with an array of characters, ranging from an effervescent housewife in The Help to a courageous Israeli spy in The Debt.

But it's Zero Dark Thirty which has put her in the big leagues with a Golden Globe win and a Best Actress Oscar nomination.

The film, the saga of a CIA agent's 10-year mission to capture Bin Laden, required an almost minimalistic performance from Chastain.

"I'm playing a character who's trained to be unemotional and analytically precise," says the actress. "As an actor, you spend your whole life trying to be emotional and keeping yourself emotionally open. So, to find the humanity within that, in that arc, was a great [challenge] for me."

Written by Mark Boal and directed by Kathryn Bigelow - the same team behind the Oscar-winning Hurt Locker - Zero Dark Thirty begins on 9/11 and ends with the shooting of Bin Laden at his compound in Abbottabad, Pakistan.

In between, the film encompasses scores of events in multiple countries, spanning nearly a decade. Since Boal and Bigelow's intention was to "capture the on-the-ground reality of this mission as truthfully and viscerally as possible", they opted to document the moral lines - including torture - that were crossed.

The saga pivots on a little-known participant in the intel hunt: Maya (Chastain), a young CIA officer who was central in tracking down Bin Laden's whereabouts. Maya is based on an actual CIA agent who remains undercover to this day.

"When I was reading the script, every page that I turned was a shock to me, especially about Maya and the role she took in [the capture of Bin Laden]," says Chastain. "Then I got upset that it was such a shock to me. Why would I assume a woman wouldn't be involved in this kind of research? The wonderful thing about working on this film is, historically, in movies, lead characters are played by women who are defined by men, whether as a love interest or as a victim of a man. Maya's not like that."

Buoyed by outstanding reviews, Zero Dark Thirty has become a leading contender for this year's Best Picture Oscar. The New York Times called it a "wrenchingly sad, soul-shaking story about revenge and its moral costs" while New York Magazine raved that it's a "phenomenal piece of action film-making".

But some critics are uncomfortable with the film's refusal to condemn interrogation techniques such as waterboarding and forcing detainees into stress positions.

Zero Dark Thirty (the title is military jargon for the dark of night, as well as the moment - 12.30am - when the Navy Seals first set foot on Bin Laden's compound) has proven so controversial that a trio of senators (Dianne Feinstein, John McCain and Carl Levin) have written a letter to Sony Pictures calling the film "grossly inaccurate and misleading in its suggestion that torture resulted in information that led to the location" of Bin Laden.

In response, Sony released a statement from Bigelow and Boal in which the film-makers' argue that they depicted "a variety of controversial practices and intelligence methods that were used in the name of finding Bin Laden. The film shows that no single method was necessarily responsible for solving the manhunt, nor can any single scene taken in isolation fairly capture the totality of efforts the film dramatises."

In some sense, Maya's development - from innocence to determination - reflects the evolution of the United States as it attempts to deal with what the film-makers call "the ruthless calculus of terrorism".

According to Chastain, the interrogation scenes, which comprise a very small portion of the film, were among the hardest to shoot.

"Those scenes, they were tough to be honest," she says. "We filmed that section of the movie in a Jordanian prison, so we weren't on a sound stage in Los Angeles. That was a tough week."

Though Zero Dark Thirty celebrates the efforts of hundreds of hard-working CIA agents to get the job done, politics are kept out of the equation.

"It's not a propaganda movie," says Chastain. "It's not, 'Go America'. It's [told] through the eyes of this woman who became such a servant to her work that she lost herself along the way.

"[After Bin Laden is killed], there's the question, 'Where does she go now?' But then also you have to ask, 'Where do we go as a country? Where do we go as a society?' I find that ending the film on that question is far more interesting than providing an answer."

Filming primarily in Jordan and India allowed the actors to feel as if they were, in Chastain's words, "immersed in the story".

Not surprisingly, Chastain did quite a bit of research before the cameras rolled. On the advice of screenwriter Boal, an investigative reporter, she read a number of books about Bin Laden, including The Looming Tower by Lawrence Wright and Osama Bin Laden by Michael Scheuer.

Chastain says she would have loved to meet the real Maya but that option has never been on the table, since Maya remains an active intelligence officer.

"I had to approach her like any other character I was playing. Any questions I could answer through the research, I did.

"But questions that I couldn't answer through research, I had to use my imagination - and Kathryn and Mark's imagination. [I think] we respect the real woman."

Born and raised in Northern California, Chastain can't remember a time when she didn't want to be an actor. She studied at the prestigious Juilliard School in New York before scoring roles in a handful of Broadway and off-Broadway productions. She also starred alongside Al Pacino in an LA production of Salome.

She made her film debut in 2010's Jolene, which was barely released in theatres. Her 2011 movies - The Help, The Debt, Texas Killing Fields, Coriolanus and Tree of Life - scored much better.

With her 2013 films in the can, including the horror film Mama and Eleanor Rigby with James McAvoy, Chastain has been starring in a Broadway revival of The Heiress, the 1947 adaptation of Henry James' 1880 novel Washington Square.

"I'm a crazy person. I think my first film came only out a year-and-a-half ago. I'm really lucky to do what I do but I'll tell you right now, it's a very strange thing to be talking about Maya and then think, 'Okay, at 6.30pm I'm going to start putting my hair in pin curls and go on stage as Catherine Sloper in The Heiress.'

"But it's a great gift. The character of Maya is very different from me because I am a very emotional girl and very sensitive. I like to have a good time. I'm very smiley. Even though she's very different, there is something that is similar and that's [that we're both] in love with our work.

"I can understand that passion, that sense of servitude. Some might say I'm nowhere near the amazing woman that Maya is, but I do understand her.